The present invention relates to a process for producing stable emulsions of at least two substantially immiscible fluids, particularly emulsions of a liquid fuel with water, and to the apparatus used in the process.
In the present description and in the claims, the expression xe2x80x9cemulsion of two substantially immiscible fluidsxe2x80x9d designates a heterogeneous system comprising a continuous phase, constituted by a first fluid (referenced to hereinafter as xe2x80x9cprimary fluidxe2x80x9d), and a dispersed phase, constituted by a second fluid (referenced to hereinafter as xe2x80x9csecondary fluidxe2x80x9d) which is substantially immiscible with the first fluid; said dispersed phase is in the form of particles (microdroplets) with an average size of less than 5 xcexcm. This system can optionally be stabilized by adding a suitable surfactant or mixture of surfactants. The term xe2x80x9cemulsionxe2x80x9d is used here to also include the above heterogeneous systems in which the dispersed phase occurs in the form of particles having very small average dimensions, generally around 1.5 xcexcm or less, for which the term xe2x80x9cmicroemulsionxe2x80x9d can also be used. The above definition also includes emulsions constituted by a plurality of primary fluids and/or by a plurality of secondary fluids, i.e., emulsions in which the dispersed phase and/or the continuous phase are constituted by mixtures of different products.
Emulsions or microemulsions of petroleum products and water, in which particular surfactants or mixtures of surfactants are used, are known in the art.
For example, U.S. Pat. No. 3,876,391 discloses water-in-petroleum type microemulsions which use a surfactant mixture constituted by a first surfactant which is soluble in the petroleum phase and a second surfactant which is soluble in the water phase, whereto a further water-soluble additive, for example an amide, an alkanolamine, a polyamine or an aldehyde, is added. U.S. Pat. No. 4,465,494 discloses microemulsions of liquid fuels with water which contain an alcohol or an amine and use a salt of an alkylphenoxyalkanoic acid as surfactant. A fuel emulsified with water is disclosed in EP-630 398 and is obtained by mixing the components in a static mixer in particular pressure and temperature conditions in the presence of a mixture of surfactants constituted by sorbitan oleate, a polyalkylene glycol, and an alkylphenoletoxylate.
In general, the use of surfactants or other additives such as those mentioned above can entail problems because they can be inherently toxic and/or corrosive with respect to the metals with which they make contact and because toxic byproducts can form during combustion. These drawbacks are particularly evident if nitrogen-containing and/or aromatic products are used. Moreover, on the basis of the Applicant""s experience, emulsions of liquid fuels and water prepared according to conventional methods by adding suitable surfactants generally entail stability problems also in optimum storage conditions; accordingly, after some time an at least partial phase separation occurs which entails many drawbacks during the combustion process due to the nonhomogeneous condition of the fuel being fed.
EP-124 061 in the name of this same Applicant discloses an apparatus and a process for forming emulsions of fluid fuels with other immiscible fluids, particularly water. The described apparatus is constituted by a turbotransducer comprising an emulsification chamber in which the fluid fuel and the water are subjected to a combined mechanical and electromagnetic action which generates, inside said chamber, a collimated corridor through which the mixed fuel and water flow. The fluids enter the emulsification chamber through an injector which imparts a turbulent motion, with a predominantly axial orientation, to the fluids. This apparatus produces a fuel for feeding burners or the like which has high energy efficiency combined with a significant decrease in polluting emissions both in terms of particulate matter and of carbon monoxide.
EP-372 353 in the name of this same Applicant discloses a process for producing stabilized emulsions of a fuel, particularly a fuel for Diesel engines, and water, with the addition of a product acting as lubricant and antifreeze, for example sorbitol monoleate. This process entails premixing the fuel, the water and the additive and then passing the resulting mixture through a turbotransducer which is similar to the one disclosed in the above-cited EP-124 061. The resulting emulsion is stable and is suitable for storage in tanks; during combustion, it has high energy efficiency and reduced toxic emissions, particularly as regards nitrogen oxides, carbon monoxide and particulate matter.
The Applicant has observed that in some cases, particularly if low-density fuels are used, the process disclosed in EP-124 061 and EP-372 353 requires a plurality of passes of the emulsion through the apparatus or the use of a plurality of apparata in series in order to transfer to the system constituted by the two immiscible liquids an amount of energy that is sufficient to break the dispersed phase, i.e. usually the water phase, into particles having dimensions which ensure high performance in terms of emulsion stability and combustion uniformity. This fact entails relatively high energy consumption and decreases the productivity of the system.
Moreover, the Applicant has observed that poor efficiency in converting the energy associated with passage through the emulsion apparatus into surface energy of the particles of the dispersed phase, and therefore in forming very fine particles, entails an overheating of the resulting emulsion (for example to temperatures above 60xc2x0 C.) which causes, in some conditions, evaporation of the lighter fractions of the fuel, with consequent loss of the fluid-dynamics stability of the system and possible irregularities or interruptions in the stream entering the turbotransducer due to cavitation in the pumping system.
The Applicant has now observed that a considerable increase in the efficiency of the emulsion-forming process can be achieved by injecting the fluids to be emulsified into an emulsification chamber provided with an injection system that imparts to the fluids a motion in a direction which is substantially perpendicular to the general direction of transit of said fluids through the emulsification chamber. This injection system can be provided by means of a diffuser provided with an inlet hole, through which a stream of liquid is fed in a substantially axial direction, and at least one outlet hole, which leads into the chamber and whose axis lies on a plane which is substantially perpendicular to the direction of the inlet stream. In this manner, the stream strikes the walls of the emulsification chamber, producing a turbulent motion of the fluids which has a predominantly helical orientation and is capable of providing efficient dispersion of one fluid in the other, forming particles of the dispersed phase having an average diameter on the order of one micron or even less.
In a first aspect, the present invention accordingly relates to a process for producing an emulsion of at least one primary fluid with at least one secondary fluid, said fluids being substantially mutually immiscible, which comprises feeding a stream of said fluids into an emulsification chamber provided with an inlet for said fluids and with an outlet for said emulsion, said inlet and said outlet being arranged along a main axis of said emulsification chamber, obtaining a stream of the emulsified fluids at the outlet;
characterized in that said process comprises imparting to the stream of said fluids that enter the emulsification chamber a motion in a direction which is substantially perpendicular to said main axis of the emulsification chamber.
In a preferred embodiment of the present invention, said process comprises imparting to the stream of said fluids entering the emulsification chamber initially a motion in a direction which is substantially parallel to the main axis and then a motion in a direction which is substantially perpendicular to the main axis.
According to a preferred aspect, said process further comprises conveying the stream of said emulsion leaving the emulsification chamber so as to achieve initially stream motion in a direction which is substantially perpendicular to the main axis and then stream motion in a direction which is substantially parallel to the main axis.
In a preferred embodiment, said process further comprises premixing the primary fluid with the secondary fluid and then feeding the resulting mix into the emulsification chamber.
In the present description and in the claims, the term xe2x80x9cstream motionxe2x80x9d defines the predominant component of the motion of the fluid threads that constitute the stream, which have a substantially turbulent orientation. This predominant component determines the general direction of stream motion.
In the present description and in the claims, the expression xe2x80x9cdirection which is substantially perpendicular to an axisxe2x80x9d means a direction which forms, with respect to said axis, an angle between 70xc2x0 and 110xc2x0, preferably between 80xc2x0 and 100xc2x0.
In the present description and in the claims, the expression xe2x80x9cdirection which is substantially parallel to an axisxe2x80x9d means a direction which forms, with respect to said axis, an angle between xe2x88x9220xc2x0 and +20xc2x0, preferably between xe2x88x9210xc2x0 and +10xc2x0.
According to a preferred embodiment of the present invention, the primary fluid and the secondary fluid are premixed by feeding a stream of the primary fluid and a stream of the secondary fluid into a premixing chamber which is provided with an inlet for the primary fluid, an inlet for the secondary fluid and an outlet for the mixture, said outlet being connected to the emulsification chamber. Preferably, said outlet and at least one of said inlets are arranged along a main axis of said premixing chamber.
According to a preferred aspect, the step of feeding the primary fluid stream and the secondary fluid stream into the premixing chamber comprises imparting motions to the two streams in substantially mutually perpendicular directions.
According to a preferred aspect, in the premixing chamber the inlet for the primary fluid and the outlet for the mixture are arranged along said main axis, while the inlet for the secondary fluid is arranged along a secondary axis of said premixing chamber which is substantially perpendicular to said main axis. According to this last embodiment, the feeding of the stream of primary fluid preferably comprises imparting to said primary fluid stream a motion in a direction which is substantially parallel to said main axis, while the feeding of the stream of secondary fluid comprises imparting to said secondary fluid stream a direction of motion which is substantially perpendicular to said secondary axis.
According to another preferred aspect, the process for producing the emulsion according to the present invention is performed in the presence of a magnetic field generated inside the emulsification chamber.
According to another aspect, the present invention relates to an apparatus for producing an emulsion of at least one primary fluid with at least one secondary fluid, said fluids being substantially immiscible with each other, said apparatus comprising an emulsification chamber provided with an inlet for said fluids and an outlet for said emulsion, said inlet being arranged along a main axis of said emulsification chamber; characterized in that said inlet comprises a diffuser provided with an inlet hole whose axis is substantially parallel to said main axis and an outlet hole whose axis is substantially perpendicular to said main axis.
According to a preferred embodiment of the present invention, said diffuser comprises a hollow cylindrical body; on the side wall of said cylindrical body through holes are provided which have a radial axis, and said cylindrical body has an end which is connected to said inlet and another end which is closed.
According to another preferred aspect, at the outlet of the emulsification chamber a conveyance device for the emulsion is provided, which has an inlet hole whose axis is substantially perpendicular to the main axis of the emulsification chamber and an outlet hole whose axis is substantially parallel to said main axis.
According to another preferred aspect, said conveyance device comprises a hollow cylindrical body; on the side wall of said cylindrical body through holes are provided which have a radial axis, and said cylindrical body has one end which is connected to said outlet and another end which is closed.
According to a preferred embodiment of the present invention, said diffuser and said conveyance device are arranged along the main axis of the emulsification chamber in a mirror-symmetrical position with respect to each other.
According to a further preferred aspect, the internal surface of the emulsification chamber is cylindrical and has a helical groove which has a predetermined depth and pitch.
The depth and the pitch of the groove are predetermined mainly as a function of the rheological characteristics of the fluids and of the flow parameters of the system.
According to a preferred aspect, the apparatus according to the present invention further comprises a premixing chamber provided with an inlet for the primary fluid, an inlet for the secondary fluid and an outlet for the resulting mixture, said outlet being connected to the inlet of the emulsification chamber. Preferably, the outlet for the mixture and the inlet for the primary fluid are arranged along a main axis of said premixing chamber, while the inlet for the secondary fluid is arranged along a secondary axis of said premixing chamber which is substantially perpendicular to said main axis. Even more preferably, said secondary fluid inlet comprises a diffuser provided with an inlet hole whose axis is substantially parallel to said secondary axis and an outlet hole whose axis is substantially perpendicular to said secondary axis.
According to a preferred aspect, the apparatus according to the present invention further comprises a compensation chamber provided with an inlet and an outlet which are arranged along a main axis of said compensation chamber, said inlet being connected to the emulsion outlet of the emulsification chamber. The compensation chamber is mainly meant to absorb any pulses of the output stream caused by the fluid pumping system. Preferably, the outlet of said compensation chamber has a conveyor which comprises a substantially cylindrical hollow body having an open end and another end which is provided with a perforated plate arranged perpendicularly to the main axis of the compensation chamber. Preferably, the inlet of said compensation chamber is provided with a diffuser which has an inlet hole whose axis is substantially parallel to said main axis and an outlet hole whose axis is substantially perpendicular to said main axis.
According to another aspect, the present invention relates to a system for producing an emulsion of at least one primary fluid with at least one secondary fluid, said system comprising:
(a) an apparatus for producing the emulsion, said apparatus comprising an emulsification chamber provided with an inlet for said fluids and with an outlet for the resulting emulsion, said inlet being arranged along a main axis of said emulsification chamber;
(b) devices for pumping the primary fluid and the secondary fluid into the apparatus;
(c) devices for extracting the emulsion that leaves the apparatus;
characterized in that said inlet of the emulsification chamber comprises a diffuser provided with an inlet hole whose axis is substantially parallel to said main axis and an outlet hole whose axis is substantially perpendicular to said main axis.
According to a particular embodiment, said system further comprises an accumulation tank for the produced emulsion.
According to another aspect, the present invention relates to a process for the production and combustion of an emulsion of a liquid fuel and water, comprising the steps of:
(a) producing the emulsion of the liquid fuel and the water;
(b) feeding said emulsion into an emulsion combustion device;
(c) performing combustion of the emulsion;
characterized in that the emulsion is produced by feeding a stream of liquid fuel and water into an emulsification chamber, so as to impart to said stream a motion in a direction which is substantially perpendicular to the general direction in which the stream passes through the emulsification chamber, with a supply pressure which produces an emulsion having predetermined characteristics in terms of dispersion of the water in the fuel.
In a first embodiment, in said production and combustion process the emulsion produced in step (a) is sent directly to the emulsion combustion device.
In another embodiment, in said production and combustion process the emulsion produced in step (a) is first sent to an accumulation tank and then fed to the emulsion combustion device.
The process according to the present invention allows to produce emulsions of liquid fuels and water in which the water is dispersed in the liquid fuel with predetermined dispersion characteristics, particularly as regards the average size of the dispersed water particles. It is believed that this characteristic is decisive in its achieving a combustion of high quality in terms of both energy efficiency and polluting emission reduction. In particular, it is believed that high-quality combustion can be achieved with an average size of the water particles dispersed in the liquid fuel of generally less than 1.5 xcexcm, preferably between 0.05 and 1 xcexcm. Moreover, the dispersion characteristics of the water in the liquid fuel directly affect the stability of said emulsion, which is a particularly critical property in the case of low-density liquid fuels (for example Diesel fuels), for which storage in tanks, also for long periods, is usually required. The stability of the resulting emulsions can be evaluated on the basis of any phase separations found after centrifuging a sample of the emulsion at a predetermined speed and for a predetermined time. It is believed that the emulsions of liquid fuels and water have a stability which is sufficient to allow to store them for long periods (more than 1 month) if they show substantially no phase separation after centrifuging at 1000 g (g=acceleration of gravity) for 15 minutes (at room temperature).